It is known to produce fireproofing glasses by filling the spaces between the panes in a multilayer laminate with a water-containing gel (so-called fireproofing laminate glasses).
Such fireproofing laminate glass panes have been in use for some time as so-called F glazing. They have the effect that, on contact with flames on one side, the side of the pane facing away from the fire ensures sealing of the room for a certain time and its temperature does not exceed about 180.degree. C. So-called G glazing only ensures room sealing for a certain time.
Known F glazing contains a layer of clear, water-containing gel between individual glass panes in the form of an optionally multilayer sandwich construction. In general, the achievable resistance time of such constructions for a given glass type and a given gel layer thickness depends on the number of individual gel intermediate layers present in the laminate.
Examples of gel layers employed are alkali metal silicate gels or gels comprising water-compatible, crosslinked organic polymers, for example of the polymethacrylic acid type. These gels have the ability to ensure the F resistance times given in each case. If, however, in the case of contact with flames the gels are dehydrated, burnt or melted at high temperature, the final pane of the laminate facing away from the flames is melted out of the frame particularly easily, and temperatures of above 600.degree. C. then prevail, so that there,is no significant resistance for longer room sealing beyond the F resistance time. This is particularly evident when inexpensive float glasses and alkali metal silicate gels are used. However, room sealing beyond the F resistance time is desired in order to achieve an extended residual protective action.
EP-B 306 677 describes, as fireproofing gels, combinations of monoaluminium hydrogen phosphate and boric acid in a weight ratio of from 10 to 25 in the form of 80% strength by weight and more highly concentrated solutions which have an extrudable, gel-like character but become molten in the event of a fire and can run out of the burst pane into the flame space, casting doubt on the protective effect.
To avoid such difficulties, DE-A 4 020 459 describes a gel system in which an acrylic acid derivative and a photoinitiator are dissolved in an aluminium phosphate solution and this solution is polymerized by exposure to light after introduction between glass panes. The polymerization to be carried out and the additional handling of acrylic monomers constitute a disadvantageous complication. In addition, this gel system tends to exhibit crystalline material causing turbidity.
DE-A 4 023 310 and DE-A 4 126 702 describe fireproofing gels of aluminium tris-phosphate ethanolamine salts, which can be used inter alia for fireproofing laminate glass panes. Such gel layers are very suitable for production without complications of fireproofing laminate glass panes but are still worthy of improvement with regard to the melt behaviour of flame application.
According to a prior proposal of the Applicant (German Application P 42 26 044.2), aqueous solutions of ethanolamine salts of aluminium phosphates are modified with 2 to 5 moles of boric acid (for example in the form of its ethanolamine salts) per mol of aluminium phosphate. If such solutions are to be used as an intermediate layer for fireproofing laminate glass panes, good results are obtained only with the addition of gel formers of other types, for example acrylamide. In the case of such systems, the boron content is relatively high and, here too, the practical necessity of additional handling of acrylic monomers and the polymerization thereof constitute a complication of the preparation process for fireproofing laminate glass panes.